Program Flow - Wahl Heat-Prober 392AHP User Manual

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Heat-Prober Platinum-RTD Thermometers User Manual

9.2 Program Flow

When Power is turned on, the program will start executing instructions from address 000, the
location of the top level program labeled "Main."
The first routine called is "Initialize". This is a house-keeping routine which establishes the
starting conditions. The data memory (RAM) is cleared, the input/output ports are configured,
and the display is set up for 0.0 reading.
Next, the routine "Gaincheck" is called. A solid state switch is confirmed to connect the AID
converter to a precision wire-wound resistor of known value. The resistor reading is compared
with the ideal value, stored in memory, and a factor is calculated and stored to be applied to
subsequent readings of the probe resistance.
Probe and Gaincheck readings are maintained in a "Moving Average" (M.A.) fashion to minimize
the effects of random variations. Gaincheck readings following "Initialize" or the detection of a
removed probe cause the moving average to be crammed with the current value. Subsequent
passes cause the moving average to be updated and refined. Gaincheck updates occur
alternately with probe readings the first 15 cycles, and then they are performed only every 20th
cycle. This is to allow more computer visibility to the probe updates with reduced inertia. Settling
time is provided to allow analog reference circuits to stabilize when the probe readings are done
on the high scale. The compensation readings are always made on the low scale.
If readings exceed the compensation limits (about 6% is allowed), the pro- gram branches to a
subroutine which displays "Help" on the second such excess.
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